1. Field of the Invention
The present invention relates to the delivery of treatment material to, and treatment of, the area contained within and around a subsea cap that protects the top of a subsea structure.
2. Description of Relevant Art
In offshore oil and gas exploration and development, a subsea well is drilled and data from the well is collected and analyzed to determine the amount of oil and gas in the area. While the data is being reviewed, drilling operations are suspended. The floating rig is disconnected from the subsea well and the subsea structure is left exposed 5 to 15 feet above the ocean floor for several months or years while the data is analyzed. This period is deemed temporary abandonment. To protect the subsea structure against falling debris and silt during this temporary abandonment, a subsea cap is installed on top of the exposed subsea structure. Critical working components of the subsea structure are guarded from corrosion via corrosion inhibitor material that is put into the stagnant area within the subsea cap via containers hung underneath the subsea cap or pumped in through an umbilical. None of these add treatment to the external profile of the wellhead which has a critical locking profile.
In addition, during suspension of a drilling operation, the well operator may return to the well to perform routine well maintenance or other work at the well site including taking measurements of internal components (such as, for example, casing hangers) and installing additional components while the drilling rig is away. In this process, the well operator deploys an ROV to the well site. The ROV is meant by way of example and is not meant to limit the scope of the invention. Other methods such as divers are also used. The ROV then descends to measure critical components inside the subsea structure. During these operations, the subsea cap must be removed and previously treated water is allowed to escape. The subsea cap is then either brought to the surface to be reloaded with new corrosion inhibitor or re-injected with corrosion inhibitor such as through an umbilical line connected or otherwise associated with one or more pumps, bladders, drums of corrosion inhibition chemicals and interfacing tools. The removal of the subsea cap to replenish the chemical under the cap leaves the structure exposed to falling objects and silt and can cause protracted ROV deployment times which in turn can lead to extended periods of down time, lengthy delays, and increased costs. Injecting fluid through an umbilical also causes delays as the ROV must surface and change tooling to accomplish this additional task, involving one or more pumps, bladders, drums of chemicals and interfacing tools.
The potential for extensive time and money loss involved in subsea cap removal and recovery, treatment-material recharging, and subsea cap replacement exhibits a clear need for a subsea cap system with the ability to be charged and recharged with treatment materials without removal, recovery and reinstallation of the subsea cap, and without additional tooling, trips to the surface and handling of chemical drums.
Therefore, it is a goal of this invention to provide an improved system to treat and maintain the internal and external working components of an exposed subsea structure while also protecting the subsea structure from falling debris and silt and from marine growth. It is also a goal of the present invention to provide an improved method of treating the area beneath a subsea cap, defined as the space within the open upper portion of a subsea structure and the area within the body of a subsea cap and the upper external profile of the subsea structure, including, but not limited to, a wellhead.
It also is an object of this invention to provide an alternative to the current method of treating stagnant areas beneath a subsea cap by fixedly suspending at least one treatment-material-loaded container from the underside of a subsea cap as described in U.S. Pat. No. 6,817,417 (invented by Blair et al. and filed Mar. 1, 2002). If there is a problem during the dive or installation, the ROV may have to return to the surface before installing the cap containing the treatment material. If the treatment material has been activated, such as from exposure to water, the treatment material can disburse into non-intended areas such as around the diver or workers trouble shooting and repairing the equipment, potentially making an unsafe work site.
Additionally, it is an object of the present invention to deliver treatment material, regardless of its current state (solid, liquid, gel, gas, etc.) and without removing the subsea cap to load or reload the treatment material, involving for example, one or more pumps, bladders, drums of chemicals, and interfacing tools. Another object is to provide a means to quickly install a replacement container if the cap has to be temporarily removed for well inspection or other reason. ROV recovery time from 5,000 feet is an average of about 100 feet per minute. If a cap has to be recovered to add more material at the surface, ascent of the ROV takes about 50 minutes, adding more material to the container (such as a basket) takes about 20 minutes, and the descent back to the subsea structure takes about another 50 minutes. It is an object of this invention to deliver and install another canister when the ROV or diver or other means goes to re-install the cap after inspection or after installing other hardware, without having to resurface for tooling or obtaining treatment material from drums. This canister installation would take a few minutes instead of the approximate 2 hours described above.
It is another object of the present invention to provide a method and system that does not require a conventional umbilical line or associated pumps, bladders, drums of chemical or interfacing tools to pump treatment material into the space beneath a subsea cap as described in U.S. Pat. No. 7,051,804 (invented by Arning and filed May 16, 2003).